Implement federation room state snapshot endpoint

lib/matrix_server/encodable_map.ex

@@ -1,6 +1,6 @@
 # https://github.com/michalmuskala/jason/issues/69
 defmodule MatrixServer.EncodableMap do
-  alias MatrixServer.{EncodableMap, Event}
+  alias MatrixServer.EncodableMap
   alias MatrixServer.Types.{UserId, RoomId, EventId, GroupId, AliasId}
 
   defstruct pairs: []

lib/matrix_server/room_server.ex

@@ -60,6 +60,10 @@ defmodule MatrixServer.RoomServer do
     GenServer.call(pid, {:server_in_room, domain})
   end
 
+  def get_state_at_event(pid, event) do
+    GenServer.call(pid, {:get_state_at_event, event})
+  end
+
   ### Implementation
 
   @impl true
@@ -104,6 +108,26 @@ defmodule MatrixServer.RoomServer do
     {:reply, result, state}
   end
 
+  def handle_call({:get_state_at_event, %Event{room_id: room_id} = event}, _from, state) do
+    room_events =
+      Event
+      |> where([e], e.room_id == ^room_id)
+      |> select([e], {e.event_id, e})
+      |> Repo.all()
+      |> Enum.into(%{})
+
+    state_set = StateResolution.resolve(event, false)
+    state_events = Map.values(state_set)
+
+    auth_chain =
+      state_set
+      |> Map.values()
+      |> StateResolution.full_auth_chain(room_events)
+      |> Enum.map(&room_events[&1])
+
+    {:reply, {state_events, auth_chain}, state}
+  end
+
   defp create_room_insert_events(room, account, %CreateRoom{
          room_version: room_version,
          preset: preset,

lib/matrix_server/state_resolution.ex

@@ -55,6 +55,12 @@ defmodule MatrixServer.StateResolution do
     |> do_resolve(room_events)
   end
 
+  def full_auth_chain(events, room_events) do
+    events
+    |> Enum.map(&auth_chain(&1, room_events))
+    |> Enum.reduce(MapSet.new(), &MapSet.union/2)
+  end
+
   defp do_resolve([], _), do: %{}
 
   defp do_resolve(state_sets, room_events) do
@@ -150,12 +156,6 @@ defmodule MatrixServer.StateResolution do
     MapSet.difference(auth_chain_union, auth_chain_intersection)
   end
 
-  defp full_auth_chain(events, room_events) do
-    events
-    |> Enum.map(&auth_chain(&1, room_events))
-    |> Enum.reduce(MapSet.new(), &MapSet.union/2)
-  end
-
   defp auth_chain(%Event{auth_events: auth_events}, room_events) do
     auth_events
     |> Enum.map(&room_events[&1])

lib/matrix_server_web/error.ex

@@ -13,6 +13,7 @@ defmodule MatrixServerWeb.Error do
       {400, "M_INVALID_ROOM_STATE", "The request would leave the room in an invalid state."},
     unauthorized: {400, "M_UNAUTHORIZED", "The request was unauthorized."},
     invalid_param: {400, "M_INVALID_PARAM", "A request parameter was invalid."},
+    missing_param: {400, "M_MISSING_PARAM", "A request parameter is missing."},
     unknown_token: {401, "M_UNKNOWN_TOKEN", "Invalid access token."},
     missing_token: {401, "M_MISSING_TOKEN", "Access token required."},
     not_found: {404, "M_NOT_FOUND", "The requested resource was not found."},

lib/matrix_server_web/federation/controllers/event_controller.ex

@@ -25,11 +25,7 @@ defmodule MatrixServerWeb.Federation.EventController do
               |> put_status(200)
               |> json(data)
             else
-              put_error(
-                conn,
-                :unauthorized,
-                "Origin server is not allowed to see requested event."
-              )
+              put_error(conn, :unauthorized, "Origin server is not participating in room.")
             end
 
           _ ->
@@ -41,5 +37,44 @@ defmodule MatrixServerWeb.Federation.EventController do
     end
   end
 
-  def event(conn, _), do: put_error(conn, :bad_json)
+  def event(conn, _), do: put_error(conn, :missing_param)
+
+  def state(%Plug.Conn{assigns: %{origin: origin}} = conn, %{
+        "event_id" => event_id,
+        "room_id" => room_id
+      }) do
+    query =
+      Event
+      |> where([e], e.event_id == ^event_id and e.room_id == ^room_id)
+      |> preload(:room)
+
+    case Repo.one(query) do
+      %Event{room: room} = event ->
+        case RoomServer.get_room_server(room) do
+          {:ok, pid} ->
+            if RoomServer.server_in_room(pid, origin) do
+              {state_events, auth_chain} = RoomServer.get_state_at_event(pid, event)
+
+              data = %{
+                auth_chain: auth_chain,
+                pdus: state_events
+              }
+
+              conn
+              |> put_status(200)
+              |> json(data)
+            else
+              put_error(conn, :unauthorized, "Origin server is not participating in room.")
+            end
+
+          _ ->
+            put_error(conn, :unknown)
+        end
+
+      nil ->
+        put_error(conn, :not_found, "Event or room not found.")
+    end
+  end
+
+  def state(conn, _), do: put_error(conn, :missing_param)
 end

lib/matrix_server_web/federation/http_client.ex

@@ -66,6 +66,13 @@ defmodule MatrixServerWeb.Federation.HTTPClient do
     Tesla.get(client, path)
   end
 
+  def get_state(client, room_id, event_id) do
+    path =
+      RouteHelpers.event_path(Endpoint, :state, room_id) |> Tesla.build_url(event_id: event_id)
+
+    Tesla.get(client, path)
+  end
+
   defp tesla_request(method, client, path, request_schema) do
     with {:ok, %Tesla.Env{body: body}} <- Tesla.request(client, url: path, method: method),
          %Ecto.Changeset{valid?: true} = cs <- apply(request_schema, :changeset, [body]) do

lib/matrix_server_web/router.ex

@@ -65,6 +65,7 @@ defmodule MatrixServerWeb.Router do
     scope "/v1" do
       get "/query/profile", QueryController, :profile
       get "/event/:event_id", EventController, :event
+      get "/state/:room_id", EventController, :state
     end
   end